In common mobile communication networks two main techniques for a data transmission are used: circuit switched data transmission and packet switched data transmission. In the circuit switched domain a network establishes an interconnection for data transmission by allocating a radio channel to a mobile station, when a network host or service provider intends to transmit data via the network. Then data is transmitted via the network after the interconnection has been established. The radio channel is occupied by the mobile station during the entire duration of the interconnection, even though in many cases only a small amount of data has to be transmitted. However, regularly a subscriber is charged for the entire duration of the interconnection. This type of circuit switched data transmission is used in GSM (Global System for Mobile communications) networks.
In the packet switched domain the network transmits a data packet only when required, i.e. when data transmission has to be carried out. Thus, several mobile stations can use the same radio channel at a time. If a mobile station generates a data packet, the network routes that packet via a first unattached radio channel to a recipient. Thus, as data transmission frequently consists of data bursts, the radio channels can be used in an efficient manner. This type of packet switched data transmission is used in GPRS (General Packet Radio Service) and UMTS systems.
Recent packet data terminal devices (or user equipments (UEs) in 3rd generation (3G) mobile communication terminology) enable access to the Internet and to intranets. Therefore, the GPRS data transmission uses particularly the internet protocol (IP). If a mobile station is attached to a GPRS system and a PDP (Packet Data Protocol) context is activated, a terminal equipment is able to send data packets via the mobile station to the uplink. Vice versa, a host can use the downlink to send data packets to the terminal equipment. These data packets are routed by a gateway GPRS support node (GGSN) and a serving GPRS support node (SGSN) to the correct addresses.
However, before sending data packets the mobile station has to carry out a GPRS attach and a PDP context activation. The GPRS attach informs the network that the mobile station is available. The attach is established by the mobile station and the SGSN. Furthermore, after the GPRS attach is established, the mobile station carries out a PDP context activation. The PDP context activation makes the mobile station known to the corresponding GGSN. Thereupon, data transmission via the GGSN to external networks is enabled. Such PDP context activation may be requested by either the network or the mobile station.
In UMTS systems, a PDP context preservation functionality is provided which enables the core network (CN), e.g. an SGSN, to release corresponding radio access bearers (RABs) of a UE or the whole signaling connection of the UE, but keeps the PDP context in active state. I.e., the PDP context remains active in UE and in the CN, although the corresponding RAB resources are released. In general, the term “radio access bearer” may be used to identify a service the so-called access stratum (AS) provides to the so-called non access stratum for transfer of user data between the UE and the CN. The NAS is a functional layer running between the UE and the CN. The layer supports traffic and signaling messages between the CN and the UE. The function of the AS is to support the NAS. This includes the functions and protocols for the transport of information across the access network (e.g. UMTS Terrestrial Radio Access Network (UTRAN)) and the air interface.
Furthermore, the Iu interface is an open Interface connecting the UTRAN to the CN. The function of the Iu interface includes split responsibility and services towards the CN, handles time alignments, error control, initialization etc. The Iub interface is located between a radio network controller (RNC) and a base station (or “Node-B” in 3G terminology). Via the Iub interface, the RNC controls the Node-B. For example, the RNC allows the negotiating of radio resources, adding and deleting of cells controlled by the individual Node-B, or supporting the different communication and control links. One Node-B can serve one or multiple cells.
Paging channel (PCH) states allow the UE to go back to sleep and just be awake periodically to receive incoming pages and/or perform cell update procedures if the neighboring cell quality exceeds the serving cell quality by a certain threshold. In these states, no user data transfer can take place.
The PDP context preservation can be triggered only by a RAB release request procedure or by a Iu release request procedure initiated by the RAN. So far, the UE has no proper way to trigger an RAB or Iu release without PDP context deactivation. Thus, in order to release a RAB or Iu, the UE can only use a PDP context deactivation procedure or a GPRS detach procedure (which causes automatic context deactivation). PDP context related procedures are described in more detail in the 3GPP specifications 24.008 V7.6.0. (2006-12). GPRS detach procedures are described in more detail in the 3GPP specifications 23.060 V7.3.0. (2006-12).
To keep PDP context(s) active, some UEs may be driven to use a radio resource context (RRC) signaling connection release indication procedure is described in the 3GPP specification 25.331, which forces the network to release the whole signaling connection (over Iu and evidently also over the Iub interface). However, if many UEs use this method, it may cause network problems or at least a huge amount of useless signaling. As an example, some UEs or services (e.g. Blackberry) have used the RRC signaling connection release indication procedure. Motivations behind this could be e.g. that such UEs have not implemented mandatory PCH states at all and/or one brutal way to save battery of the UE in a network which does not support PCH states. However, PCH states will be even more crucial for the 3G networks in the future and also for network strategy.